Of course you'll have to find out for sure where your brake line is leaking before you can fix anything. Brake fluid dissolves in water so you could spray everything clean, allow to dry and find the source easier than if everything's covered with brake fluid. I've found that for fuel tank and fuel line work, sometimes it's easier to lift the truck bed to access the fuel tank area, this may be a good way to get to the brake lines but I'd have to look myself to see, you may have to move the tank anyway. First find out exactly where the leak is..